MAP direct correlation to FE?

[oldtamiyaphile]

I've personally never found a car that went open loop at 80% load. My Renault will go open loop at 100% load plus a bit more pedal. My Wrangler will only go open loop above 90km/h. Even with an older car and MPGuino I didn't see enrichment at full load.

My Fiat will stay closed loop at all loads/ speeds. I suspect it does enrichment even though the loop indicator suggests closed. For the other cars, I believe the loop indicators to be correct.

[Occasionally6]

The enrichment is done only when it is useful to prevent knock. When that occurs isn't constant but varies with engine speed and load.

As far as staying in closed loop at all loads and speeds, we need a clearer definition of "closed loop". It simply means the ECU is using exhaust gas composition as a feedback input to refine the air:fuel ratio.

With narrow band O2 sensors, anything other than stoichiometric mixtures must be open loop due to the inability of this type of sensor to accurately reflect mixtures away from this ratio. "Open loop" is proxy for "rich" at high loads but can be lean at light loads.

A wide band type sensor can be used at any air:fuel ratio to provide feedback so it's possible, indeed likely, that it is always used closed loop.

[pgfpro]

sword_guy8

IMO I think what you are seeing when in high gear is a low air velocity at the intake port that creates poor fuel atomization. The 3rd gear has a higher rpm that increases port air velocity while still maintaining good load or higher MAP pressure and reduces pumping losses.

On my car I can maintain any A/F ratio at any load due to my engine management system. I have done some testing to see how far I can load the engine at different rpm's. I have large intake ports that flow great numbers for HP reasons but suffer when it comes down to low rpm high load fuel efficiency. So there is a point on every engine where it has a happy place when it comes to load and rpm.